Photoactive Pt II and Pd II complexes of N , N -diethyl- N ′-3,4,5-trimethoxybenzoylthiourea: synthesis, crystal structures, DFT and cytotoxicity studies

Photo-chemical isomerism of the cis -[Pd II /Pt II (L-κ S , O ) 2 ] complexes of N , N -di-ethyl- N ′-3,4,5-trimethoxy-benzoylthiourea (HL) in acetonitrile reversibly produces geometric trans -[Pd II /Pt II (L-κ S , O ) 2 ] isomers in solution after irradiation with visible light, as determined by 1 H NMR, UV-vis and reverse phase chromatography (RP-HPLC). Single-crystal X-ray diffraction studies reveal that the new trans -[Pd II /Pt II (L-κ S , O κ S , O ) 2 ] complexes crystallize in a triclinic P 1̄ space group, with the sulfur and oxygen donor atoms arranged trans to each other in the six-membered chelate. Structural analysis of the cis - and trans -[Pd II /Pt II (L-κ S , O ) 2 ] complexes performed using time-dependent DFT at the B3LYP/CEP31-G level of theory reveals that the cis -[Pd II /Pt II (L-κ S , O ) 2 ] complexes are more stable than their trans -[Pd II /Pt II (L-κ S , O ) 2 ] counterparts. The cytotoxicity of the HL ligand and its corresponding cis -[Pd II /Pt II (L-κ S , O ) 2 ] and trans -[Pd II (L-κ S , O ) 2 ] complexes was investigated against the human prostate cancer cell line (DUI45) and the normal embryonic kidney cell line (HEK-293). Cytotoxicity was evident after complexation with the HL ligand. In particular trans -[Pd II (L-κ S , O ) 2 ] and cis -[Pt II (L-κ S , O ) 2 ] complexes produced a significant dose-dependent decrease in cell viability of both cell lines. cis -[Pt II (L-κ S , O ) 2 ] presented the most cytotoxic activity against DUI45 and comparable selectivity to doxorubicin, a commonly used anticancer drug, indicating its potential as a Pt-based anticancer compound.